Air and fuel control for burners



D. H. MGCORKLE 2,539,789

AIR AND FUEL CONTROL FOR BURNERS Jan. 30, 1951 Filed May 26, 1947INVENTOR DONALD h. MC coma:

his A T TORNE Y Patented Jan. 30, 1951 2,539,789 AIR. AND FUEL, CoN'rRoLFOR nuances Donald; McCorkle, Berkeley, Galifi, assignor to D. H.'McCorkle 00., Berkeley, Calif., a corporation of California ApplicationMay 26, 1947, Serial No. 750,609

1 Claim. 1'

The invention relates to a means of regulating the volume of airdelivered to a vaporizing burner; and more particularly to a means forautomatically regulating the amount of air delivered to the burner whenoperating on high fire, and means for regulating a smaller volume of airwhen the burner is operating on low fire.

One of the objects of this invention is to provide a simple, reliableand inexpensive means of automatically controlling the amount of airadmitted to a burner blower. Another object is to provide automaticallyoperating means for independently adjusting the amount of air admittedto the blower on high fire and on low fire. A further object is toprovide a thermostatically controlled means for automatically reducingthe speed of the motor on low fire and increasing the speed on high fireand controlling the volume of air admitted to the blower on high speedand low speed by utilizing the difference in static pressure developedby the blower on high speed and low speed.

The invention possesses other objects, some of which with the foregoingwill be set forth at length in the following description wherein isexplained that form of the invention which has been selected forillustration in the drawings accompanying and forming a part of thisspecification. In said drawings, one form of the invention is shown, butitis to be understood that it is not limited to that form, since theinvention as set forth in the claim may be embodied in a plurality offorms.

It is common practice to use a blower in conjunction with a vaporizingoil burner, and to provide a thermostatic means arranged so that whenthe thermostat is satisfied, the fire will be reduced to a very low orpilot flame. When the thermostat calls for heat, the fire isautomatically increased to full capacity. It will readily be seen that.in this type of burner, the regulation of the draft is highly important.If, when the burner isoperating on high fire, too much air is admittedto the burner, the stack losseswill be proportionately high. On. theother hand, if. too little air is admitted, improper combustion results;and the heat exchange surfaces are soon coated with carbon, thusreducing the efiiciency of the appliance. On the pilot flame, with theadmission of too much air, there is a serious danger of extinguishingthe small flame. If insuflicient air is supplied to the burner duringthe pilot fire stage, the burner will soot and carbonize, thus reducingits efiiciency on high fire. It is common practice to carry a pilot firein excess of actual needs to prevent extinguishment. this often resultsin delivering heat to the rooms when such heat might be objectionable;My invention is calculated to obviate these undesirable features.

It is general practice to provide a smallcentrifugal b-0wer connecteddirectly to a fractional horsepower shaded pole motor. It is importantto note that in this type of blower the static pressure varies with thespeed of the rotor, and that in a shaded pole motor; particularly of"the size used on vaporizing burners, the speed may be reduced byinserting resistance in series in the feed line. However, when the speedis reduced below approximately 40% of normal, it becomes erratic andundependable. In my invention I vary the speed of the motor, but do notreduce such speed below a controllable point.

Referring to the attached drawings: Figurel is a side view of a burnerinstallation embodying my invention. Figure 2 is a front view, partly insection and showing the air control means. The electric circuits andmechanism for controlling the circuits and fuel valve are shown indiagram in Figure 3.

A typical burner installation in which myair 'control devices areembodied comprises a vaporizing burner 2, supplied with fuel throughpipe 3. in which the conventional control valve 4 is interposed. Thisvalve generally has a built-in adjustable by-pass so that when the valveis in the 0ffp0siti0n a small amount of fuel is fed through the supplyline to the burner to maintain a pilot fiame. A conventional form ofblower it forces air through the duct l to the burner; and is driven bythe shaded pole motor 3, directly connected thereto. The motor issupplied by the feed lines 9 and iii, in one side ll of which a switch[2 and a resistance iii are inserted. When the switch is closed theresistance is shunted out and the motor runs at its rated speed. Whenthe switch is open, the resistance cuts the voltage down so that themotor runs at a calcu ated. lower speed consistent with thenexistingconditions of fuel supply.

Fixed against the inlet side of the fan housing is the casing l6, havingin the side thereof, a swinging shutter l1 suitably pivoted on ananti-frictional bearing 18. To the upper end of the shutter and on theoutside thereof is fixed a lever arm I9, the upper end of which isthreaded to mount a threaded counterweight 2|.

The proportion and arrangement of parts is such that the counterweightmay be adjusted to place the center of gravity of the shutter structureon the inner side of its pivotal support. Also fixed on the shutter atits upper end but on the inside is a stop arm 22 arranged to engage theend of an adjusting screw 23, threaded into the top wall 24 of thecasing it. By turning the adjusting screw the inward swing of theshutter may be limited to regulate the amount of air which can pass theshutter into the casing. Swing of the shutter in the other direction islimited by the adjusting screw 26 threaded into the upwardly turned edge21 of the casing. Thus both maximum and minimum passages into the casingare provided; and these are automatically controlled by the staticpressure determined by the fan speed, such fan speed of coursecorresponding to the motor speed.

Means are provided for varying the motor speed and also the amount offuel supplied to the burner, in response to temperature changes in thespace heated by the apparatus of which the burner Z is a part.

A room thermostat 3|, Figure 3 is connected to the secondary of astandard transformer 32, supplied by the house current over lines 33.The figure indicates the position of the component parts when thethermostat is satisfied. Assuming the room temperature to drop, thethermostat will close the contact 34 completing the low voltage circuit36 which includes a suitable resistor heater 31. Heat radiated from theresistor heats a bimetal strip 38, rigidly secured to a fixed support39.

As the temperature of the bimetallic strip rises, it flexes upwardly;raising the adjusting screw 4| from the end of the lever arm 42 which ispivotally mounted on the pin 43, and is urged downward by spring 44. Thelever is connected to the valve stem 45 of the fuel control valve 4,either directly as shown or by simple linkage; and is also operativelyconnected to the switch i2 by which the high voltage circuit through themotor is closed. As the adjusting screw 4! rises, the spring loaded endof the arm moves downward. In so doing, the connecting device opens thevalve 4 to admit the required amount .of fuel to maintain the burner onhigh fire. At the same time the switch 12' closes the motor circuit,shunting out the fixed resistor I3, and :allowing the motor 8 to developits full rated R. P. M.

When the room thermostat is satisfied, the contact 34 is opened, theheat resistor 3'1 cools, .the bimetal strip 38 returns to the positionshown in the figure, and the rocker arm 42 moves to partially close thevalve to pilot fire, and open the switch l2, so that the fixed resistorI3 is once more in series with the motor, thus reducing its speed to thedesired R. P. M. It is important to note that the resistor is soselected as to reduce the speed of the motor, buthot to such a point asto result in erratic and undependable speed. When the motor is thusoperating at low speed, the static pressure created by the blower iscorrespondingly reduced; and the shut- ..ter- I1. rests against theadjusting screw 26 which static pressure.

is set at a point to supply the proper amount of air to the burner onpilot fire. The counterweight 2| is then set at a point where theshutter will bear lightly against the end of the adjusting screw.

On the high fire phase, the thermostat 3| closes the circuit, and asexplained, the switch 12 shorts out the fixed resistor; and the motoroperates at full R. P. M. This increase in motor speed results in anincrease of static pressure. As the shutter I! has been nearly balancedfor the low fire stage, the added static pressure will cause the shutterto swing inwardly until the arm 22 engages the lower end of theadjusting screw 23, which has been set to admit the proper amount of airat high fire.

It will be seen from the above that the amount of air admitted on highfire can be adjusted independently of the amount of air admitted on lowfire; and that the amount of air admitted on .low fire 15 subject toadequate control independently of the control of the motor speed.

My invention permits the control of this air from complete shut-off tothe full amount that would be admitted to the blower at the lower It isalso to be noted that the volume of air admitted to the blower on fullstatic pressure can be regulated from full capacity of the blower to apoint equal to the low fire setting.

I claim:

An air and fuel control device for a fuel burner, comprising a fan fordelivering air to the burner and having an air intake passage, a movablegate for varying the size of said intake passage, supporting said gatefor movement by pressure of air flowing through said passage, a valvefor controlling the flow of fuel to said burner, means responsive tochanges in temperature of a space to be heated for varying the speed ofthe fan from a low speed to a high speed and vice versa and the settingof the valve whereby the How cl fuelincreases and decrease respectivelywith iii-- REFERENCES orrsn The following references are of record inthe file of this patent:

UNITED STATES PATENTS Num er Name Date 1,655,246 Schermully Jan. 3, 19281,741,529 Marion Dec. 31, 1929 2,187,045 McCorkle Jan. 16, 19402,251,055 Howard et a1. July 29, 1941 2,351,878 Russell June 20, 19442,370,891

Thornquist Mar. 6, 1945

